JP6835913B2 - Methods and systems for self-testing MEMS inertial sensors - Google Patents

Description

The technique described in this application relates to a microelectromechanical system (MEMS) inertial sensor.

An inertial sensor is an electronic device that uses one or more accelerometers and / or gyroscopes to measure and report motion, force, angular velocity, and / or other quantities. MEMS gyroscopes may be configured to detect angular motion by sensing the acceleration caused by the Coriolis force generated as the resonant mass of the gyroscope undergoes angular motion. The MEMS accelerometer can be configured to sense linear and / or angular acceleration.

One aspect of the disclosure relates to a technique for self-testing a microelectromechanical system (MEMS) inertial sensor. Some such techniques involve testing the properties of the inertial sensor, such as the sensitivity of the accelerometer to acceleration and the sensitivity of the gyroscope to angular motion. The test can be performed by providing the MEMS inertial sensor with a test signal that simulates a stimulus such as acceleration or angular velocity, and by examining the output of the sensor. The effectiveness of such self-testing can be compromised by spurious signals that can be present in the sensor environment and can affect the output of the sensor. Therefore, the self-testing techniques described herein involve detecting the presence of such spurious signals and discarding the self-test results when their presence is detected. In some embodiments, the presence of a spurious signal can be detected by using a signal obtained by mixing the response of the MEMS inertial sensor with a reference signal that is substantially orthogonal to the test signal.

Another aspect of the disclosure relates to a system for testing a microelectromechanical system (MEMS) inertial sensor. The system consists of a signal generator configured to stimulate the MEMS inertial sensor using the test signal and a test circuit, a response signal obtained from the MEMS inertial sensor with an in-phase reference signal in response to the test signal. To generate an in-phase response signal by mixing with, generate an orthogonal response signal by mixing the response signal with an orthogonal reference signal, and the in-phase response signal to evaluate the characteristics of the MEMS inertial sensor based on the orthogonal response signal. If it is determined that it should be used and the in-phase response signal should be used to evaluate the characteristics of the MEMS inertial sensor, then the in-phase response signal should be used to evaluate the characteristics of the MEMS inertial sensor. It may be equipped with a test circuit configured in.

Another aspect of the disclosure relates to a method for testing a microelectromechanical system (MEMS) inertial sensor. The method is to stimulate the MEMS inertial sensor using a test signal, to receive a response signal from the MEMS inertial sensor in response to the stimulus, and to generate an in-phase response signal using the response signal and the in-phase reference signal. To generate an orthogonal response signal using the response signal and the orthogonal reference signal, and to determine whether the in-phase response signal should be used to characterize the MEMS inertial sensor based on the orthogonal response signal. It may include using the in-phase response signal to evaluate the characteristics of the MEMS inertial sensor if it is determined that the in-phase response signal should be used to characterize the MEMS inertial sensor. ..

Another aspect of the disclosure relates to a system for testing a microelectromechanical system (MEMS) inertial sensor. The system is a MEMS inertial sensor and a test circuit that uses the test signal to stimulate the MEMS inertial sensor, receives a response signal from the MEMS inertial signal in response to the stimulus, and uses the response signal and the in-phase reference signal. The in-phase response signal should be generated using the response signal and the orthogonal reference signal to generate the orthogonal response signal, and the in-phase response signal should be used to evaluate the characteristics of the MEMS inertial sensor based on the orthogonal response signal. If it is determined that the in-phase response signal should be used to evaluate the characteristics of the MEMS inertial sensor, the in-phase response signal is configured to evaluate the characteristics of the MEMS inertial sensor. , With a test circuit.

Various aspects and embodiments of the present application will be described with reference to the following figures. It should be understood that the figures are not necessarily drawn at constant scale. Items that appear in multiple figures are indicated by the same reference number in all figures in which they appear.
FIG. 6 is a block diagram illustrating an exemplary system for testing a MEMS inertial sensor according to some embodiments of the techniques described herein. FIG. 6 is a schematic representation of an exemplary MEMS accelerometer that can be tested using the exemplary system of FIG. 1 according to some embodiments of the techniques described herein. FIG. 6 is a schematic representation of an exemplary MEMS gyroscope that can be tested using the exemplary system of FIG. 1 according to some embodiments of the techniques described herein. FIG. 6 is a flow diagram of an exemplary method for testing a MEMS inertial sensor according to some embodiments of the techniques described herein. FIG. 6 is a block diagram of an exemplary response analyzer that can be used together within the exemplary system of FIG. 1 according to some embodiments of the techniques described herein. A table showing how an exemplary response analyzer of FIG. 4 can process the output of a MEMS inertial sensor in response to application of a test signal, according to some embodiments of the techniques described herein. Is.

Self-testing is a technique used in electronics to assess whether an electronic device is operating according to its specifications or deviating from its expected behavior, and deviation is the repair or replacement of the device. May indicate equipment problems that may need to be addressed by doing so. An important advantage of self-testing is that it is performed after the electronic device has been installed and / or deployed, after manufacture and under the control of the manufacturer, and possibly without even the need to disrupt its normal operation. Is what you can do.

A MEMS inertial sensor is an example of an electronic device that can be self-tested after it has been installed and / or deployed. MEMS inertial sensors such as accelerometers and gyroscopes are devices manufactured using microfabrication techniques. Due to their mechanical nature, these devices are sensitive to external environmental conditions such as large temperature fluctuations, pressure changes, and / or large mechanical vibrations, which can result in poor performance, partial or total. May require regular maintenance, including replacement. Self-testing is an effective technique for determining when and when maintenance and replacement of MEMS components should be performed.

The inventor has recognized that conventional techniques for self-testing MEMS inertial sensors can be improved because MEMS inertial sensors are susceptible to the presence of environmental noise and / or other spurious signals. .. In particular, the inventor of the present invention has poor performance of the MEMS inertial sensor due to the presence of noise in the system (in this case, no repair is required) in the circuits conventionally used for self-testing the MEMS inertial sensor. Recognized that the ability to discern (which may indicate that repair or replacement is needed) is limited. As a result, conventional self-testing techniques result in false warnings, which can cause MEMS inertial sensors to be flagged as unsatisfactory performance in the absence of real problems. For example, a test of a MEMS accelerometer mounted on a car can give a false warning if the driver sounds a bell during the test. When the driver sounds the alarm, it causes acoustic vibration that can be inadvertently interpreted as the acceleration to be measured by the MEMS accelerometer. As a result, the output of the MEMS accelerometer in the car can reflect the vibration of the alarm, and if this occurs during the self-test cycle, the output of the MEMS accelerometer will deviate from the expected behavior, so the MEMS device Can be misinterpreted as indicating the problem of.

Some embodiments of the techniques described herein relate to techniques and systems for performing self-testing of MEMS inertial sensors that reduce or eliminate the above-mentioned problems of conventional self-testing techniques. Specifically, some embodiments relate to techniques for determining if the test results are distorted by the presence of noise or other spurious signals. If it is determined that there is a significant spurious signal that can distort the test results, the test results can be discarded.

In some embodiments, the presence of a spurious signal, which can significantly affect the accuracy of the test, causes the MEMS inertial sensor to be orthogonal to (or uncorrelated with) the expected test signal response when excited by the test signal. It can be detected by determining whether to respond with a non-minor signal. Under quiet conditions, for example, in an ideal scenario where there is no spurious signal, the MEMS inertial sensor should not emit a response signal that is orthogonal to the expected test signal response. Therefore, as described in more detail below, when the output of the inertial sensor is demodulated to detect the orthogonal or uncorrelated signal, the result can result in a response that is substantially equal to zero. Therefore, the presence of a non-minor orthogonal response signal can be interpreted as a sign that a significant spurious signal is present. In this case, the test circuit may notify the user that the test results should be discarded, or may simply wait until the orthogonal response signal disappears or drops below a predetermined threshold. The types of test signals described herein may be configured such that the MEMS inertial sensors under test perceive them as mechanical stimuli, such as acceleration and / or angular motion.

If it is determined that there is no significant spurious signal, the test results can be considered accurate. For example, if the test results show that the accelerometer's sensitivity to acceleration is unsatisfactory, the user can be relatively convinced that the accelerometer's sensitivity is actually unsatisfactory. In some embodiments, determining whether the characteristics of the MEMS inertial sensor are satisfactory and therefore that the MEMS inertial sensor is functioning properly with respect to that characteristic is to determine when the MEMS inertial sensor is excited by the test signal. May include determining whether to respond with a signal in phase with the test signal that is close enough to the expected value. Examples of properties that can be evaluated using the techniques described herein include, but are not limited to, the sensitivity of the MEMS inertial sensor to acceleration or angular motion.

FIG. 1 is a block diagram of an exemplary system for self-testing a MEMS inertial sensor according to some embodiments of the techniques described herein. The system of FIG. 1 includes a MEMS inertial sensor 100, a notch filter 121, and a test circuit 104. The test circuit 104 may be configured to self-test the MEMS inertial sensor 100 so that the MEMS inertial sensor can be tested without human intervention or simply without the user's request. Being a self-testing system, in some embodiments, the MEMS inertial sensor 100 may be deployed with the test circuit 104 so that the entire system can test the operating performance of the MEMS inertial sensor. In some embodiments, the test circuit 104 may be configured to automatically perform the test at one or more predetermined times without input from the user. For example, in some embodiments, the test circuit 104 may be configured to test the MEMS inertial sensor 100 on a regular basis and / or according to a schedule. In other embodiments, the test circuit 104 may be configured to test the MEMS inertial sensor 100 in response to a user request. In some embodiments, the test circuit 104 may be configured to test the MEMS inertial sensor 100 without interrupting its normal operation (eg, while the MEMS gyroscope is detecting angular motion). , Or when the MEMS accelerometer is detecting acceleration). Additional or alternative, the test circuit 104 may be configured to test the MEMS inertial sensor 100 during one or more periods during which the normal operation of the MEMS inertial sensor is stopped.

In some embodiments, the MEMS inertial sensor 100 may include any suitable type of microfabrication sensor including, but not limited to, one or more accelerometers and / or one or more gyroscopes. In some of the embodiments where the MEMS inertial sensor 100 includes one or more accelerometers, the accelerometers (s) are centered on linear accelerations in 1, 2, or 3 directions and / or 1, 2, or 3 axes. It may be designed to detect the angular acceleration. An accelerometer is a sensor for detecting the movement of one or more proof masses, and the proof masses (s), which are configured to move in response to acceleration (eg, move, turn, and / or rotate). (For example, a capacitance sensor) may be included.

FIG. 2A shows an example of an accelerometer that can be included in the MEMS inertial sensor 100 according to some embodiments of the techniques described herein. Although the exemplary accelerometer 240 is configured to sense out-of-plane linear acceleration, not all embodiments are limited in this regard. The accelerometer 240 includes a proof mass 250 connected to the underlying substrate 242 via an anchor 252. The accelerometer further includes an electrode 254 formed on the top surface of the underlying substrate. Together with the proof mass 250, which can be made of at least partially conductive material, the electrode 254 forms a capacitance sensor. When the accelerometer is subjected to acceleration in the direction towards the top surface of the substrate 242 (label "A"), the proof mass 250 responds and swivels around the anchor. As a result, the distance between the proof mass 250 and the electrode 254 changes, changing the capacitance of the capacitance sensor. The magnitude of the acceleration A can be determined based on the change in capacitance.

In some of the embodiments in which one or more gyroscopes are included in the MEMS inertial sensor 100, the gyroscope (s) are configured to detect angular motion velocities around one, two, or three axes. May be done. In these embodiments, the drive circuit may be used to control the operation of the gyroscope (s). For example, the drive circuit may provide the gyroscope with a drive signal that is arranged to drive the resonator of the gyroscope. In some embodiments, the drive signal may drive the gyroscope's proof mass to swing in one direction (eg, the x-axis). When the gyroscope undergoes an angular motion about one axis (eg, the x-axis), the proof mass may move in another direction (eg, the y-axis). Angular motion may be detected based on this motion (eg, based on the range of motion of the proof mass).

An exemplary gyroscope that can be included in the MEMS inertial sensor 100 is shown in FIG. 2B. In this example, the gyroscope 200 is configured to resonate in a direction parallel to the x-axis and detect a Coriolis force in a direction parallel to the y-axis. It should be understood that the types of gyroscopes described herein are not limited to any particular resonance or detection direction.

In some embodiments, the gyroscope 200 includes a fixed frame 210 (fixed to the underlying substrate via an anchor 214), a proof mass 202, and a fixed electrode 220. The proof mass 202 is elastically connected to the fixed frame 210 via a coupler 212. The coupler 212 may be obedient and thus allows the proof mass 202 to move relative to the fixed frame 210. In this example, the proof mass 202 functions as a resonator of the gyroscope. Therefore, when a drive signal (provided by the drive circuit) is applied to one or more electrodes (not shown in FIG. 2B) connected to the proof mass 202, the proof mass 202 rocks in the x-axis direction. Move.

In some embodiments, the proof mass 202 comprises a plurality of free end beams 222 forming a plurality of sensing capacitors having their respective fixed electrodes 220. The capacitance of the sensing capacitor varies depending on the acceleration of the proof mass in the y-axis direction. When the gyroscope 200 is subjected to angular motion about the x-axis and the proof mass 202 is driven to swing along the x-axis (by a drive signal generated by the drive circuit), it is along the y-axis. A Coriolis force is generated, and the proof mass moves along the y-axis. The angular motion velocity can be determined by detecting the acceleration of the proof mass 202 along the y-axis.

With reference to FIG. 1 again, the end user may receive the signal generated by the MEMS inertial sensor 100 in response to acceleration and / or angular motion. For example, the response signal may be generated in response to capacitance fluctuations of the capacitor formed between the electrode 254 and the proof mass 250 (FIG. 2A), or the response signal was experienced by sensor 204. It may be generated in response to the Coriolis force (Fig. 2B). As further described below, the output of the MEMS inertial sensor 100 may be filtered using a notch filter 121.

In some embodiments, the test circuit 104 may be deployed to test the operating characteristics of the MEMS inertial sensor 100. For example, the test circuit 104 may be configured to generate a test signal to be applied to the MEMS inertial sensor 100 and determine how the MEMS inertial sensor 100 responds, based on the response. It is determined whether the inertial sensor 100 is operating properly. The test signal may mimic the presence of acceleration and / or angular motion. For example, in connection with the accelerometer of FIG. 2A, the test circuit 104 may use an electrostatic transducer 101 to move the proof mass 250 by electrostatic attraction or repulsion. In connection with FIG. 2B, the test circuit 104 may apply a test signal to move the proof mass 202 along the y-axis to simulate the presence of Coriolis force.

As shown in FIG. 1, the test circuit 104 includes a signal generator 110, an adder 111, an in-phase signal generator 112, an orthogonal signal generator 114, mixers 116 and 118, and a response analyzer 122. The signal generator 110 is configured to generate a test signal. In some embodiments, the signal generator 110 may be configured to output as a test signal a periodic waveform such as a periodic square wave or sine wave, or a sequence of pseudo-random numbers. The fundamental frequency of the periodic waveform is referred to as f _1. In some embodiments, f ₁ may be 500 Hz or 1 KHz, but the application is not limited to any particular frequency. For example, f ₁ may be 250 Hz to 2 KHz, 250 Hz to 1.5 KHz, 500 Hz Hz to 1 KHz, 250 Hz to 750 Hz, or any range within such a range.

The test signal may be converted into a mechanical stimulus via the electrostatic transducer 101, which can be implemented, for example, by applying a voltage across the accelerometer proof mass 250 and the working electrode 254. The output of the electrostatic force transducer 101 may be combined with an inertial force to be measured (such as acceleration and / or angular motion), for example using an adder 111. The combined force may be provided to the inertial sensor 100 as an input.

In some situations, the test circuit 104 may test the operation of the MEMS inertial sensor 100 when the MEMS inertial sensor 100 is not subjected to any external inertial force. In other situations, the test circuit 104 may test the operation of the MEMS inertial sensor 100 when it is being subjected to inertial forces. In any case, the response signal represents the response of the MEMS inertial sensor to the received input, whether it is a test signal, inertial force, noise or other spurious signal, or any combination thereof.

In some embodiments, the response signal may be filtered by the notch filter 121 before being provided to the end user to prevent detection of the response to the test signal. The notch filter 121 may exhibit a blocking band approximately centered on the fundamental frequency of the test signal. Therefore, the notch filter 121 may include an input for receiving the test signal and a circuit that sets the frequency of the blocking band based on the fundamental frequency of the test signal.

In some embodiments, the mixer 116 receives and mixes (eg, multiplies) the response signal and the common mode reference signal. The homeomorphic reference signal is substantially homeomorphic to the test signal (or correlates with the test signal if it contains a pseudo-random sequence). For example, the common mode reference signal is −π / 30 to π / 30, −π / 20 to π / 20, −π / 10 to π / 10, or any range within such a range with respect to the test signal. It may have a phase difference. The in-phase signal generator 112 may be used to bring the in-phase reference signal substantially in-phase with the test signal. The in-phase signal generator 112 may include, for example, a phase-locked loop. In some embodiments, however, _{the value of f 1} may be low enough that a simple conductive wire may be sufficient rather than the phase-locked loop used. In some of these embodiments, the test circuit 104 may behave as a lumped constant circuit such that the signal propagating inside the test circuit exhibits a slight phase change. As the test circuit 104 behaves as always lumped constant circuit, in at least some embodiments, the value of f ₁ may be selected to be lower than 5 KHz. However, in other embodiments, it may be desirable to operate the test circuit 104 at a higher frequency in order to prevent interference with low frequency noise such as 1 / f noise. The disadvantage is that the phase of the signal can change as it propagates inside the test circuit 104. In these embodiments, the common mode signal generator 112 may establish a desirable phase relationship between the test signal and the common mode response signal.

In some embodiments, the mixer 118 receives and mixes the response signal and the orthogonal reference signal. The orthogonal reference signal is configured to be substantially orthogonal to the test signal (or, if the test signal is a pseudo-random sequence, uncorrelated to it). For example, the orthogonal reference signal is an absolute value of π / 2-π / 30 to π / 2 + π / 30, π / 2-π / 20 to π / 2 + π / 20, π / 2-π /. It may have a phase difference of 10 to π / 2 + π / 10, or any range within such a range. The orthogonal signal generator 114 uses, for example, a phase shifter to set the phase of the test signal to π / 2-π / 30 to π / 2 + π / 30, − (π / 2), among other possible values. −π / 30) to − (π / 2 + π / 30), π / 2-π / 20 to π / 2 + π / 20, − (π / 2-π / 20) to − (π / 2 + π / 20), π It may be configured to shift by / 2-π / 10-π / 2 + π / 10 or − (π / 2-π / 10) to − (π / 2 + π / 10).

In some embodiments, a signal obtained by mixing a response signal and an in-phase reference signal (referred to as an in-phase response signal), and a signal obtained by mixing a response signal and an orthogonal reference signal (referred to as an orthogonal response signal). ) Is provided to the response analyzer 122 as an input. The response analyzer 122 determines whether the received signal should be used as a sure sign of the characteristics of the MEMS inertial sensor 100. For example, response analyzer 122, the response to the test signal of the MEMS inertial sensor 100, spurious signals or mechanical stimulation in the frequency f ₁ (for example, noise or other types of signals) to determine whether the impaired by the presence of May be good. If it is determined that the response of the MEMS inertial sensor 100 to the test signal is not impaired, the response analyzer 122 may evaluate the characteristics (s) of the MEMS inertial sensor 100.

In some embodiments, the orthogonal response signal may be used to determine if the response signal is influenced by a spurious signal other than the test signal. Since it is substantially orthogonal to the test signal, the amplitude of the orthogonal response signal is negligible when the test signal is applied but there is no spurious signal in the system. Therefore, if the amplitude of the orthogonal response signal is significant (eg, higher than a particular threshold), it is likely that a spurious signal is present in the system. At the same time, since it is in-phase with the test signal, the in-phase response signal directly reflects the response of the MEMS inertial sensor to the test signal. Homeomorphic response signals can also be affected by the presence of spurious signals. Therefore, if the orthogonal response signal is used and the system is determined to be substantially free of spurious signals, the common mode response signal may be used as a measure of the characteristics (s) of the MEMS inertial sensor. .. For example, the common mode response signal is used to evaluate whether the sensitivity of the MEMS inertial sensor 100 to acceleration or angular motion is within an acceptable range, and / or whether the test results should be used or discarded. May be used to

Although not shown in FIG. 1, the test circuit 104 may include a plurality of signal generators 110, and the fundamental frequency of the test signal generated by each signal generator is different from the fundamental frequency of the other test signals. .. In this way, the MEMS inertial sensor 100 may be tested with a plurality of test signals having different frequencies. The advantage is that even if one test signal is compromised by the presence of spurious signals at the same frequency, it is highly unlikely that there will be spurious signals in the environment at all multiple frequencies of all test signals. is there. In some of these embodiments, the test circuit 104 may include a mixer 116 and a mixer 118 for each of the generated test signals. Homeomorphic and orthogonal response signals at various frequencies may be provided to the response analyzer 122. The response analyzer 122 may detect the presence or absence of a spurious signal at each received frequency. The frequency (s) determined by the response analyzer 122 that no significant spurious signal is present may be used to test the MEMS inertial sensor with the corresponding common mode response signal.

FIG. 3 shows an exemplary process 300 for testing the operation of a MEMS inertial sensor according to some embodiments of the techniques described herein. In some embodiments, process 300 may be performed by the exemplary system 100 described in connection with FIG. Process 300 may be performed in an environment where a MEMS inertial sensor is deployed. For example, process 300 may be performed by a system deployed in the vehicle or in an industrial machine. Process 300 is initiated at act 302, where the MEMS inertial sensor is stimulated using the test signal. The test signal may be generated by the test circuit to simulate a MEMS inertial sensor (eg, by acceleration and / or angular velocity). In some embodiments, the signal generator 110 of FIG. 1 may generate a test signal for action 302.

In action 304, a response signal is received from the MEMS inertial sensor in response to the stimulus. In act 306, the common mode response signal is generated using the response signal and the common mode reference signal. For example, the common mode response signal may be generated by mixing the response signal and the common mode reference signal. The common mode reference signal may be substantially in phase with the test signal. In some embodiments, the mixer 116 of FIG. 1 may generate a homeomorphic response signal for action 306.

In act 308, an orthogonal response signal is generated using the response signal and the orthogonal reference signal. For example, the orthogonal response signal may be generated by mixing the response signal and the orthogonal reference signal. The orthogonal reference signal may be substantially orthogonal to the test signal. In some embodiments, the mixer 118 of FIG. 1 may generate an orthogonal response signal for action 306.

In action 310, it may be determined whether the response of the MEMS inertial sensor to the stimulus should be used as a reliable measure of the characteristics (s) of the MEMS inertial sensor. For example, based on the orthogonal response signal, it may be determined whether the common mode response signal should be used as a measure for evaluating the characteristics (s) of the MEMS inertial sensor. In effect, Act 310 may indicate the presence of spurious stimuli within the self-test system. As further discussed below, in at least some embodiments, this determination may be accomplished by assessing whether the amplitude of the orthogonal response signal is above or below the threshold. In some embodiments, the response analyzer 122 of FIG. 1 may determine whether the common mode response signal should be used as a measure for evaluating the characteristics (s) of the MEMS inertial sensor.

If it is determined that the common mode response signal should not be used as a measure of the characteristics of the MEMS inertial sensor, process 300 may continue to repeat the cycles of actions 302-310. The cycle may continue, for example, until it is determined that the common mode response signal should be used as a measure of the characteristics (s) of the MEMS inertial sensor. Optionally, in act 311 an output signal indicating that the result of the self-test is unbelievable may be output. The output signal may indicate that the results of the self-test should be ignored.

If it is determined that the common mode response signal should be used as a measure of the characteristics of the MEMS inertial sensor, process 300 proceeds to action 312 and the characteristics of the MEMS inertial sensor (s) are evaluated. The characteristics of the MEMS inertial sensor that can be evaluated include the sensitivity of the accelerometer to acceleration centered on a specific direction or axis, the sensitivity of the gyroscope to angular motion speed centered on a specific axis, and / or MEMS inertia. The band or dynamic range of the sensor includes, but is not limited to. For example, it may be determined whether the characteristic of the MEMS inertial sensor is greater than the threshold representing the acceptable minimum value of the characteristic, the acceptable minimum value may be set by the user, or the system depending on the context. May be set automatically by. In other embodiments, the characteristics of the MEMS inertial sensor may be compared to a set of thresholds. Depending on where the value of the property is relative to the threshold, the system may notify the user to what extent the MEMS inertial sensor deviates from the desired behavior.

If it is determined that the characteristics of the MEMS inertial sensor are satisfactory, eg, higher than the threshold, process 300 may transition to or complete action 313. At action 313, a signal is output indicating that the MEMS inertial sensor is functioning properly with respect to the characteristics evaluated at least in action 312. However, if it is determined that the characteristics of the MEMS inertial sensor are unsatisfactory, eg, lower than the threshold, process 300 may transition to action 314, with a notification signal indicating that the MEMS inertial sensor is malfunctioning. It may be output (eg, it may be displayed, or it may be communicated to the user in some other way). In some embodiments, process 300 may notify the user how malfunctioning the MEMS inertial sensor is with respect to its properties, eg, with a 0-10 measuring rod (or any other suitable measuring rod). This may be accomplished, for example, by comparing the common mode response signal to a set of thresholds. Process 300 may then be terminated or another cycle may be performed.

Process 300 may be performed using any suitable type of test signal. In some embodiments, process 300 may be performed using multiple test signals of different frequencies. In this way, the reliability of the method can be improved, as it is less likely that all frequencies will be disturbed by spurious signals at the same time than in a single frequency scheme.

In some embodiments, the response analyzer 122 is used as a reliable measure for assessing the characteristics (s) of the MEMS inertial sensor by comparing the amplitude of the orthogonal response signal to a threshold. You may decide whether it should be. For example, if the amplitude of the orthogonal response signal is smaller than the threshold, the response analyzer 122 may determine that there is no spurious signal that significantly interferes with the frequency (s) of the test signal (s). Therefore, this common mode response signal should be used as a solid measure for assessing the characteristics (s) of the MEMS inertial sensor. On the other hand, if the amplitude of the orthogonal signal is greater than the threshold, the response analyzer 122 states that the spurious signal is interfering with the operation of the test circuit 104, and that the in-phase response signal is characteristic of the MEMS inertial sensor (s). It may be determined that it should not be used for reliable evaluation.

In some embodiments, when it is determined that the common mode response can be used reliably to evaluate the characteristics (s) of the MEMS inertial sensor, this evaluation uses the amplitude of the common mode response signal as a threshold. It may be accomplished by comparison. This threshold value may represent the acceptable minimum value of the characteristics of the MEMS inertial sensor being evaluated. Therefore, if the amplitude of the homeomorphic inertial sensor is less than the threshold, the response analyzer 122 may determine that the MEMS inertial sensor is malfunctioning and, at least in some embodiments, may notify the user. .. On the other hand, when the amplitude of the homeomorphic inertial sensor is greater than the threshold, the response analyzer 122 may determine that the MEMS inertial sensor is functioning properly with respect to its properties. In some embodiments, the amplitude of the common mode response signal may be compared to multiple thresholds. The result may indicate the degree to which the MEMS inertial sensor is malfunctioning.

FIG. 4 shows an exemplary implementation of the response analyzer 122 according to some embodiments of the techniques described herein. In this example, the response analyzer 122 includes comparators 402 and 404, as well as logic unit 410. The comparator 404 may receive the orthogonal response signal and the threshold value t1 as inputs and generate an output based on the comparison between the amplitude of the orthogonal response signal and the threshold value. The output of the comparator 404 may depend, for example, on whether the amplitude of the orthogonal response signal is greater than or less than the threshold t1. In some embodiments, when the output of the comparator 404 indicates that the amplitude of the orthogonal response signal is greater than the threshold t1, the logic unit 410 compromises the results produced by the test circuit 104 at the frequency of the test signal. It may be determined that it is.

The comparator 402 may receive the common mode response signal and the threshold value t2 as inputs and generate an output based on the comparison between the amplitude of the common mode response signal and the threshold value t2. The output of the comparator 402 may depend, for example, on whether the amplitude of the common mode response signal is greater than or less than the threshold t2. In some embodiments, the logic unit 410 may determine that the MEMS inertial sensor is malfunctioning if the output of the comparator 402 indicates that the amplitude of the common mode response signal is less than the threshold t2.

The mode in which the logic unit 410 can handle the outputs of the comparators 402 and 404 is depicted in the table of FIG. As shown, when the amplitude of the orthogonal response signal is greater than or equal to the threshold t1 (whether the amplitude of the in-phase response signal is greater than or less than the threshold t2), the logic unit 410 is tested at the corresponding test signal frequency. It may be programmed to determine that it is impaired by the presence of the signal.

The logic unit 410 may be further programmed to determine that the MEMS inertial sensor is functioning properly if the amplitude of the orthogonal response signal is less than the threshold t1 and the amplitude of the in-phase response signal is greater than the threshold t2. .. On the other hand, the logic unit 410 may be programmed to determine that the MEMS inertial sensor is malfunctioning if the amplitude of the orthogonal response signal is less than the threshold t1 and the amplitude of the in-phase response signal is less than the threshold t2. ..

Aspects of the techniques described herein may provide one or more advantages, some of which have already been described above. Some examples of such advantages are described below. It should be understood that not all embodiments and embodiments provide all of the benefits described below. Moreover, it should be understood that aspects of the techniques described herein may provide additional benefits in addition to the benefits described below.

Aspects of the techniques described herein provide a method of self-testing a MEMS inertial sensor. For example, some embodiments are configured to assess whether the MEMS inertial sensor is functioning properly or malfunctioning, or, in some embodiments, the degree to which the MEMS inertial sensor is malfunctioning. .. Other aspects of the technique described herein provide an indication of whether the results of self-testing should be ignored or trusted, eg, due to the presence of spurious signals.

100 Inertivity sensor 101 Electrostatic force transducer 104 Test circuit 110 Signal generator 111 Adder 112 In-phase signal generator 114 Orthogonal signal generator 116 Mixer 118 Mixer 121 Notch filter 122 Response analyzer 200 Gyroscope 202 Proof mass 204 Sensor 210 Fixed frame 212 Coupler 214 Anchor 220 Fixed electrode 222 Free end beam 240 Accelerometer 242 Board 250 Proof mass 252 Anchor 254 Electrode 402 Transducer 404 Transducer 410 Logic unit

Claims (20)

Microelectromechanical system (MEMS) A system for testing inertial sensors.
It ’s a test circuit,
Upon receiving a response signal representing the response of the MEMS inertial sensor to the test signal generated by the signal generator,
An in-phase response signal is generated by mixing an in-phase reference signal that is in-phase with the test signal with the response signal.
An orthogonal response signal is generated by mixing the response signal with an orthogonal reference signal that is orthogonal to the test signal.
Based on the orthogonal response signal, it is determined whether the common mode response signal should be used to evaluate the characteristics of the MEMS inertial sensor.
When it is determined that the in-phase response signal should be used to evaluate the characteristics of the MEMS inertial sensor, the in-phase response signal is configured to evaluate the characteristics of the MEMS inertial sensor. A system, equipped with a test circuit. The system according to claim 1, wherein the in-phase reference signal and the test signal are substantially in-phase with each other. The system of claim 1, further comprising a phase shifter configured to make the orthogonal reference signal and the test signal substantially orthogonal to each other. The test circuit comprises a comparator, and the test circuit at least partially compares the amplitude of the orthogonal response signal with the threshold amplitude in the first comparator so that the in-phase response signal is characteristic of the MEMS inertial sensor. The system of claim 1, configured to determine if it should be used to evaluate. If it is determined based on the orthogonal response signal that the in-phase response signal should not be used to evaluate the characteristics of the MEMS inertial sensor, the test circuit ignores the results of the self-test. The system of claim 1, further configured to output a notification signal indicating that it should be. The system of claim 1, further comprising a signal generator configured to stimulate the MEMS inertial sensor using the test signal. A method for testing microelectromechanical system (MEMS) inertial sensors.
Using the test signal to stimulate the MEMS inertial sensor,
Receiving a response signal from the MEMS inertial sensor in response to the stimulus
Using an in- phase reference signal that is in-phase with respect to the response signal and the test signal to generate an in-phase response signal,
Using an orthogonal reference signal that is orthogonal to the response signal and the test signal to generate an orthogonal response signal,
Based on the orthogonal response signal, determining whether the common mode response signal should be used to evaluate the characteristics of the MEMS inertial sensor.
When it is determined that the in-phase response signal should be used to evaluate the characteristics of the MEMS inertial sensor, the in-phase response signal is used to evaluate the characteristics of the MEMS inertial sensor. Including methods. The method of claim 7, further comprising making the in-phase reference signal and the test signal substantially in-phase with each other. The method of claim 7, further comprising making the orthogonal reference signal and the test signal substantially orthogonal to each other. Determining whether the in-phase response signal should be used to evaluate the characteristics of the MEMS inertial sensor based on the orthogonal response signal determines if the amplitude of the orthogonal response signal is lower than the first threshold amplitude. 7. The method of claim 7, comprising doing so. The method of claim 7, wherein evaluating the characteristics of the MEMS inertial sensor using the in-phase response signal comprises determining whether the amplitude of the in-phase response signal is higher than the second threshold amplitude. 11. The method of claim 11 further comprises outputting a notification signal indicating that the MEMS inertial sensor is malfunctioning if the amplitude of the common mode response signal is not greater than the second threshold amplitude. the method of. The method of claim 7, wherein the characteristics of the MEMS inertial sensor include sensitivity to acceleration of a MEMS accelerometer or sensitivity to angular motion of a MEMS gyroscope. Microelectromechanical system (MEMS) A system for testing inertial sensors.
With the MEMS inertial sensor
It ’s a test circuit,
In response to the test signal, a response signal is received from the MEMS inertial signal,
An in-phase response signal is generated using the response signal and an in- phase reference signal that is in phase with the test signal, and an orthogonal response signal is used using the orthogonal reference signal that is orthogonal to the response signal and the test signal. To generate
Based on the orthogonal response signal, it is determined whether the common mode response signal should be used to evaluate the characteristics of the MEMS inertial sensor.
When it is determined that the in-phase response signal should be used to evaluate the characteristics of the MEMS inertial sensor, the in-phase response signal is configured to evaluate the characteristics of the MEMS inertial sensor. A system with a test circuit and. 14. The system of claim 14, wherein the test circuit is further configured to make the in-phase reference signal and the test signal substantially in-phase with each other. 14. The system of claim 14, wherein the test circuit is further configured to make the orthogonal reference signal and the test signal substantially orthogonal to each other. The in-phase response signal evaluates the characteristics of the MEMS inertial sensor by the test circuit determining at least in part whether the amplitude of the orthogonal response signal is lower than the first threshold amplitude based on the orthogonal response signal. 14. The system of claim 14, configured to determine if it should be used to. The test circuit is configured to evaluate the characteristics of the MEMS inertial sensor using the in-phase response signal by, at least in part, determining if the amplitude of the in-phase response signal is higher than the second threshold amplitude. The system according to claim 14. Further, when the test circuit determines that the amplitude of the in-phase response signal is not higher than the second threshold amplitude, it outputs a notification signal indicating that the MEMS inertial sensor is malfunctioning. The system according to claim 18, which is configured. 14. The system of claim 14, wherein said characteristics of the MEMS inertial sensor include sensitivity to acceleration of a MEMS accelerometer or sensitivity to angular motion of a MEMS gyroscope.